A hard disk drive (HDD) is equipped with a magnetic recording medium and a magnetic head; the magnetic head reads and writes data on the magnetic recording medium. The magnetic head in the HDD is constituted by a recording head for recording information on the magnetic recording medium (magnetic disk) as magnetic signals and a reproducing head for reading out signals recorded on the magnetic recording medium as magnetic signals. The reproducing head includes a magnetoresistive effect stacked body consisted of a plurality of magnetic thin films and non-magnetic thin films and is called a magnetoresistive effect head because it reads signals by utilizing magnetoresistive effect.
There have been various types of stacking structures for magnetoresistive effect heads, and the heads are classified into categories such as an AMR head, a GMR head, a CPP-GMR head, and a TMR head in accordance with the principle of the magnetic resistance used therein. They use a magnetoresistive effect (AMR), a giant magnetoresistive effect (GMR), a current perpendicular plane GMR effect (CPP-GMR effect), a tunnel magnetoresistive effect (TMR), respectively, and retrieve input magnetic fields entering the reproducing head from the magnetic recording medium as voltage changes.
Currently, development in high sensitivity has required a reproducing scheme with higher sensitivity. In the range of 70 to 150 (Gb/in.2), the TMR head which has a very high MR ratio is advantageous in view of improvement of sensitivity. The TMR head is disclosed in Japanese Patent Publication No. 3-154217 (“Patent Document 1”), for example.
For ultra high recording density exceeding 150 (Gb/in.2), the CPP-GMR head or the like may be preferred. The CPP-GMR is disclosed in Japanese Unexamined Patent Application No. 11-509956 (“Patent Document 2”), for example. Being different from the current in plane GMR (CIP-GMR) in which sense current flows parallel to film planes of the magnetoresistive effect stacked body, the TMR and the CPP-GMR are schemes in which the sense current flows perpendicular to the film planes, i.e., in the direction of stacking the film planes. In the present specification, the scheme like this is referred to as a CPP scheme; and the reproducing head like this, a CPP reproducing head.
FIG. 17(a) is a cross-sectional view schematically showing a configuration of the CPP reproducing head 71. The magnetoresistive sensor 712 is provided between a lower shield 711 and an upper shield 713. The lower shield 711 and the upper shield 713 function as magnetic shields and a lower electrode and an upper electrode respectively as well for supplying the magnetoresistive sensor 712 with sense current. Under the upper shield 713, an upper magnetic isolation film 714 made of a conductor is provided.
As shown in FIG. 17(b), the magnetoresistive sensor 712 includes a sensor underlayer 271, an antiferromagnetic film 272, a fixed layer 273, a non-magnetic intermediate layer 274, a free layer 275, and a sensor cap film 276 sequentially stacked from the lower layer side. Exchange interaction with the antiferromagnetic film 272 works on the fixed layer 273 so that the magnetization direction is fixed. If the reproducing head 71 is a TMR head, the non-magnetic intermediate layer 274 is formed of an insulator such as alumina (AL2O3) or magnesium oxide (MgO). If a CPP-GMR is used, the non-magnetic intermediate layer 274 is formed of a non-magnetic conductor such as a Cu alloy. The track width of the free layer 275 is denoted by Twf.
If the relative magnetization direction of the free layer 275 to the magnetization direction of the fixed layer 273 changes due to the magnetic field from the magnetic disk, the resistance (current value) of the magnetoresistive sensor 712 changes. Thereby, the reproducing head 71 can detect an external magnetic field. On the right and left of the magnetoresistive sensor 712, hard bias films 715 are provided. The bias fields from the hard bias films 715 act on the free layer 275 to have a single magnetic domain. The hard bias film 715 is formed on the hard bias underlayer film 716. As a lower layer of the hard bias underlayer film 716, a junction insulating film 717 is formed. The insulating film 717 is provided between the hard bias underlayer film 716 and a lower shield film 711 and the magnetoresistive sensor 712 and works for the sense current not to flow outside of the magnetoresistive sensor 712.
Next, manufacturing steps of the CPP reproducing head 71 will be described. First, a multilayer film constituting the magnetoresistive sensor 712 is deposited and formed by sputtering. Then, a resist is formed by resist coating and patterning and a track width of the multilayer film magnetoresistive sensor 712 is formed by etching using ion milling. Then, the insulating film 717 is formed. Furthermore, the hard bias underlayer film 716 and the hard bias film 715 are formed. Then, the resist is lifted off and the upper magnetic isolation film 714 and the upper shield film 713 are formed.
In the above etching step of the magnetoresistive sensor 712, the side ends of the magnetoresistive sensor 712 are exposed to etching particles. At this time, an etching damaged layer 781 is formed on the exposed surfaces as shown in FIG. 17(b). It has now been revealed that the etching damaged layer 781 formed on the end of the magnetoresistive sensor 712 in this etching step impairs characteristics and reliability of the magnetoresistive sensor 712. Specifically, it has now been revealed that shunt current flowing in the etching damaged layer 781 becomes a significant problem. Therefore, it is required to suppress the etching damages in the etching step of the magnetoresistive sensor 712.
In the CPP reproducing head 71, thicknesses and shapes of the respective layers in vicinity of the end of the magnetoresistive sensor 712 are important as well as the insulating voltage-resistant characteristic of the insulating film 717. For example, the hard bias film 715 having a conventional structure shown in FIG. 17(a) is formed thicker near the side end of the magnetoresistive sensor 712 and the film thickness gradually increases from near the end of the magnetoresistive sensor 712. Thus, near the side end of the magnetoresistive sensor 712, a large level difference Ush is formed on the upper shield 713 and the upper shield 713 has a shape having a deep depressed part on the magnetoresistive sensor 712.
This results in upper shield 713 not being flattened, or that the flattened width becomes smaller on the magnetoresistive sensor 712. If the flattening of the upper shield 713 is not enough for the track width Twf of the free layer like this, a problem occurs in that the effect of the upper shield 713 at the end of the magnetoresistive sensor 712 is reduced so that a spread width in reading increases. In particular, this problem is obvious in a reproducing head with a small shield space Gs.